1. Field of the Invention
This invention relates to a jig for measuring an object shape such as a lens and a method for measuring a three-dimensional shape for use in a measurement device such as a three-dimensional shape measurement device, which determine, according to the relative position between the front and back surfaces of the object, an eccentricity and an inclination between the front and back surfaces.
2. Description of the Related Art
Well-known conventional methods for determining an eccentricity and an inclination of front and back surfaces of a lens include the following technologies. JP 2006-78398 discloses a measurement method in which an object-holding jig is provided that allows for a measurement of an object from its front and back surface sides, the object-holding jig is used to measure three-dimensional shape data of a lens and the central point coordinates of three reference balls, the three-dimensional shape data of the lens front and back surfaces are combined based on the central point coordinates of the reference balls, and an eccentricity and an inclination between the lens front and back surfaces are computed from the combined data of the lens front and back surfaces.
In the measurement method disclosed in the above document, the three-dimensional shape is measured for the three reference balls to obtain the central point coordinates, the central point coordinates are then used to align the three-dimensional measurement data of the lens front and back surfaces, and the eccentricity and the inclination between the vertexes of the lens front and back surfaces are measured. In this method, unfortunately, it takes a long time for the entire three-dimensional measurement because it takes a long time particularly to measure the three-dimensional shapes of the reference balls.